Vacuum switch



A. LODGE Nov. 20, 1962 VACUUM SWITCH Filed Feb. 2'7, 1961 INV EN TOR.

United States Patent 3,064,322 VACUUM SWlTCH Alvin Lodge, Erie, Pa., assignor to American Sterilizer Company, Erie, Pa., a corporation oi? Pennsylvania Filed Feb. 27, 1961, Ser. 91,714 3 Claims. (Ql. 21-94) In sterilizers it is desirable that the sterilizing chamber be evacuated before introducing the sterilizing agent to insure prompt and uniform penetration of the load. At the high vacuums required (e.g. 15-20 mm. of mercury absolute pressure), ordinary vacuum switches require barometric compensation and are so sensitive that they are both expensive and unreliable. In a preferred form this invention overcomes this problem by substituting for the ordinary vacuum switch a thermostat responsive to the boiling point of water. As the pressure within the sterilizing chamber is reduced, the boiling point of water is correspondingly reduced and upon reaching the point corresponding to the desired vacuum, the switch operates. This provides a vacuum switch with a high degree of accuracy and which does not require any barometric compensation. The boiling point of water at 15 mm. to 20 mm. of mercury absolute ranges from 63.5 to 71.9 degrees F. Thermostats operating in this range of temperature are very common and reliable.

In the drawing, FIG. 1 is a diagrammatic view of a sterilizer equipped with the vacuum switch and FIG. 2 is an enlarged view of the vacuum switch construction.

The invention is shown applied to a sterilizer having a chamber 1 with a door 2 at one end and vacuum and steam lines 3 and 4 respectively controlled by valves 5 and 6. After the material to be sterilized is loaded into the chamber, the door 2 is closed and the valve 5 is opened to connect the vacuum line 3 to the chamber. When the desired degree of vacuum is reached, the valve 5 is closed and the valve 6 is opened to discharge steam to the chamber. These and other operations incident to the operation of the sterilizer are performed in the desired sequence by a suitable control 7 connected in power line 8. The parts so far described are or may be of common construction.

In order to secure uniformity in the sterilizing cycle, it is desirable that the admission of steam be delayed until the desired vacuum in the chamber is reached. This requires a vacuum switch which will operate reliably in the range of 15 mm. to 20 mm. of mercury and at these low pressures, the available vacuum switches are expensive and unreliable. In order to provide a reliable vacuum switch, there is provided a well 9 outside the sterilizer connected through the lower end of a T 10 to a line 11 leading to the upper part of the sterilizer chamber. The upper end of the T is closed by a plug 12. The line 11 has a slight pitch draining to the well 9. When steam is admitted to the sterilizing chamber, a small amount bleeds through the line 11 and is condensed by the cooling efiect of the ambient air. The condensate drains into the well 9, keeping it filled with water. In the well 9 is a thermostat bulb 13 controlling a switch (diagrammatically indicated at 14) within the casing 15 on which the thermostat is mounted. Having the well 9 connected to the sterilizing chamber insures ?atented Nov. 20, 1962 that the well will be kept filled with water. During each steam sterilizing cycle, the steam flows through the line 11 and is condensed by the cooling eifect of the ambient air. If the vacuum switch were used in other applications, other arrangements could be used to fill the well with water.

When the chamber 1 is evacuated at the start of the sterilizing cycle, the vacuum above the surface of the water in the well 9 is the same as the vacuum in the sterilizing chamber because the well and chamber are always connected by the line 11. As the vacuum becomes higher, the boiling point of the water in the well drops and finally reaches the temperature for which the thermostat 13 is set. At this point, the switch 14 is closed, starting the sterilizing control. The desired vacuum Within the chamber 1 is in the range of from 15 to 20 mm. which corresponds to a thermostat setting in the range of from 64 to 71.9 degrees F. Thermostats in this range are accurate, cheap and reliable.

In use, the load to be sterilized is loaded into the chamber 1 and the door 2 closed. Valve 5 is then opened to connect the vacuum.- line to the chamber. When the desired vacuum is reached, the vacuum switch closes, starting the control 7 to perform the operations incident to the sterilizing cycle.

What is claimed as new is:

1. In a sterilizer having a sterilizing chamber with means for evacuating the chamber and a switch to be operated when the vacuum in the chamber reaches a predetermined value, a well filled with water, a line connected from above the liquid level in the well to the chamber, and a thermostat immersed in the Water for operating the switch as the boiling point of the water in the well reaches the temperature corresponding to said predetermined value of vacuum.

2. A vacuum switch comprising a well filled with liquid which boils at temperatures within the ranges of vacuum at which operation of the switch is desired, a. line connecting the well to the source of vacuum, and a thermostatic switch responsive to the temperature of the liquid in the well.

3. In a sterilizer having a sterilizing chamber with means for supplying steam to the chamber, means for evacuating the chamber prior to the admission of steam, and a switch to be operated when the vacuum in the chamber reaches a predetermined value, a well outside the chamber, a line from the well to a part of the chamber above the well so that steam from the chamber is condensed by the cooling effect of the ambient air and maintains the well filled with water, and a thermostat immersed in the water for operating the switch as the boiling point of the water in the well reaches the temperature corresponding to said predetermined value of vacuum.

References Cited in the file of this patent UNITED STATES PATENTS 2,208,552 Walter July 16, 1940 2,715,251 Vischer Aug. 16, 1955 FOREIGN PATENTS 608,614 Canada Nov. 15, 1960 

